Field of the Invention
The invention relates to an apparatus for examining moving products, especially moving piece goods, by x-ray.
Description of Related Art
For safety reasons piece goods, in particular containers filled with a medium, are checked in production lines mostly for the presence of foreign objects. Inspection systems suitable for this purpose often operate with x-rays, which penetrate the piece goods or rather the filled container and in doing so generate image data that enable the detection of foreign objects. It is understood that not only can foreign objects be detected in this manner, but characteristics of the piece goods or of the medium in the container in question, or of the container itself, can also be checked. For example, the presence and position of bones in pieces of meat or the percentage of fat in pieces of meat can be determined because different materials or substances absorb the x-rays penetrating the piece goods differently and thus damp the x-rays differently as well. It is also possible to assess the fullness of a filled container and check whether it is filled to a minimum fill level, for example.
Such x-ray inspection apparatuses typically operate with an x-ray beam that expands in a fanlike manner from an x-radiation source, which penetrates the piece goods to be inspected. The x-radiation source for this purpose is often mounted on the side of a conveyor device, for example a belt conveyor, so that the fanlike x-ray beam penetrates the piece goods from the side. On the other side of the conveyor device provision is made of a detector device, which detects the x-radiation not absorbed after it has penetrated the piece goods.
The fanlike x-ray beam usually has a beam plane that runs transversely, in particular perpendicularly to the conveying direction. The spread of the beam perpendicular to the beam plane is usually slight, but dependent upon the nature of the detector device. Many times use is made of detector devices in the form of a linear detector array, which has a plurality of pixels located equidistantly along a straight line. It is understood that the longitudinal axis of such a linear detector array must be aligned with the beam plane. In this case the spread of the x-ray beam perpendicular to the beam plane only needs to correspond approximately to the width of the pixels of the linear detector array. A wider beam (the spread of the beam perpendicular to the beam plane is referred to as the width) would not result in greater sensitivity because the energy contained in the width of the beam that is no longer detected by the pixels is lost. When use is made of a linear detector array, the resolution is generally defined by the area of the individual pixels and the spacing of the pixels. The pixel area and hence also the pixel width should therefore be selected within a range that ensures that the resolution generated thereby satisfies the requirements for detection precision.
As special linear detector arrays, use can also be made of so-called time delay integration (TDI) detectors, which have several detector lines running parallel to the beam plane but supply the (integrated) signal of the individual detector lines as an output signal. In this case the beam width should be wide enough that all rows of the TDI detector are covered by the beam width.
In all such line scanners, the moving product to be examined is scanned line by line (or slice by slice). The overall image of the product (or a section thereof) can then be generated, preferably as digital information, by assembling the individual lines (which correspond to x-rayed slices of the product).
More generally, however, use can also be made of an x-ray camera as a two-dimensionally operating detector in a detector device, wherein the x-ray camera is selected with respect to the detector area such that either the whole product or a section thereof is captured in one step. It is understood that several image sections can be reassembled into a whole image here as well. In this case the selected beam width must be at least as great as the width of the sensitive area of the camera, which can be configured as a two-dimensional digital sensor.
A prior art apparatus (InspireX R50S, Mettler-Toledo) for examining moving products employs an x-radiation source that is located on the side of a belt conveyor. The position of the x-radiation source is aligned with the surface of the upper run of the belt conveyor, on which the products to be examined lie. An x-ray beam of which the lower marginal beam runs essentially parallel to the belt surface (horizontally) can thus be generated and used. The bottom region of the product is thus penetrated by an essentially horizontal partial beam (beam bundle with a small opening angle (beam width)). This is advantageous if the floor area of a glass container, for example, is to be examined for damage. The lateral spacing of the position of the x-radiation source from the belt conveyor or rather from the product to be examined and the opening angle of the x-ray beam are selected such that the whole product will be penetrated by the fanlike beam.
In this apparatus, the position of the x-radiation source can be varied horizontally such that (if the opening angle of the beam remains constant) the beam can always be set such that the minimum possible beam height (measured, for example, at the position of the product with the minimum spacing from the x-radiation source in the beam plane) will always be used for a given height and shape of the product. In other words, the x-radiation source can be positioned such that all of the radiation energy always passes through the product (in the worst-case plane of the product, which requires the maximum beam angle for a given positioning of the product by the belt conveyor in the beam plane; in other positioning of the product, it is understood that a portion of the radiation energy can go past the product). For examining products of limited height, the x-radiation source can thus be moved close to the belt conveyor, or rather to the product, whereas for taller products, the spacing of the x-radiation source must be increased.
However, a disadvantage lies in this apparatus in that the upper edge zone of the product to be examined is always penetrated by partial beams running relatively obliquely (in the beam plane) upwards. This leads to a distortion of the respective image zone that is generated by the scanning. For certain application cases it is desirable if an upper zone or a zone at a predetermined height of the product to be examined is also penetrated by an essentially horizontally running partial beam when, for example, checking the top edge of a glass container for damage, checking the correct seating of a lid, or detecting the fill level (or rather the correct fill level) of a container.
To this end, it is possible to locate the x-radiation source at the same height as the top edge of the product and to define the beam angle such that the whole lower zone of the product is also penetrated by the x-ray beam. For adaptation to products of different heights, the position of the x-radiation source can then be adjusted accordingly in the vertical direction. Such a purely vertically moveable x-radiation source, however, requires a simultaneous adjustment of the beam angle, i.e., of the opening angle of the fanlike beam such that the lower product zone is also (just barely) x-rayed. Here it is essential to prevent a situation in which a major portion of the radiation energy does not pass through the product (in the worst-case plane) or an area of interest of the product fails to be x-rayed. The adjustment of the beam angle, however, requires additional effort.
As a solution, U.S. Pat. No. 7,970,102 B2 describes an apparatus for examining moving containers by x-ray, in which use is made of two x-radiation sources and two associated detector devices. A first x-radiation source is provided on the side next to the belt conveyor at the same height as the conveyor belt or rather the bottom side of the container to be examined, wherein the lower marginal beam of the x-ray beam runs essentially horizontally and the beam opens upwardly at a predetermined beam angle in the beam plane. The beam angle can be selected such that an upper portion of the container is no longer penetrated by this x-ray beam. A second x-radiation source is located laterally next to the belt conveyor at the same height as the container in question. The beam generated by this x-radiation source has an essentially horizontally running upper marginal beam. The beam opens downward at a predetermined beam angle. The beam angle of this beam can be selected such that a lower portion of the container is no longer penetrated. In this alternative, however, it is ensured that the whole product, i.e., all portions of the container, are examined with at least one of the two x-ray beams in use, with the main (middle) section of the container even being examined by both x-ray beams. The second, upper x-radiation source can also be configured as vertically adjustable for adaptation to containers of different heights. However, the adjustability is limited because it is necessary to ensure that every portion of the container is penetrated by at least one of the two x-ray beams.
Essentially two separate scanning devices are involved here, which can be located one after the other when viewed in the conveyor direction. However, they can also be located such that the containers are x-rayed in different (e.g., vertically superimposed) planes.
However, a disadvantage of this apparatus lies in the high expense for the two scanning devices.